The present invention generally relates to the recovery of odoriferous principles from plant material by solvent extraction. More specifically, it relates to preparation of oleoresins from fresh plant material and even more specifically to the solvent extraction of the fresh foliage of coniferous trees.
In particular, this invention relates to the recovery of aromatic resin from fresh foliage of coniferous evergreens which contain substantial quantities of maltol (2-methyl-3-hydroxy-4-pyrone). Maltol is a heterocyclic aromatic chemical used extensively in flavor and fragrance compositions. The resin obtained by the process described in the present invention can be used as an ingredient in flavor or fragrance compositions or as a commercial source for the recovery of natural maltol.
The recovery of aromatic principles from plant material through solvent extraction has in the past been achieved using materials such as olive oil and various liquid fats as well as wine, and in more modern times using a variety of solvents such as ethyl alcohol, acetone, hexane and petroleum ether.
Hundreds of botanical species are used as raw materials and in each case a particular part of the plant such as leaves, stems, bark, fruit or flowers are found to be most suitable. Despite the variety of plant sources and the multitude of solvents that can be used in the extraction process, all known methods have one common basis. This is a preferential solubility and affinity of the aroma determining substances for the chosen solvent. The process of extraction is, in fact, preferable diffusion of aroma carrying chemicals from the plant material into a solvent phase. The chemicals can be concentrated and recovered from the solvent phase by stripping, usually through a distillation process.
Numerous extraction means used for contacting plant material with the solvent are designed to speed up and intensify the diffusion process. Despite the multitude of botanical sources and known extraction techniques, they can be divided into two major groups--those which use dehydrated plant material and those in which the oleoresin is extracted from fresh plant tissues. Cinnamon bark, black pepper, various fruits of the Umbelliferae family such as cumin, caraway, celery, etc. can be used as examples of plant material which is extracted dry. Rose flowers, jasmine, tuberose and lavender are examples of plant material which is extracted fresh.
Hardy raw materials which are mentioned in the first group usually retain their aromatic values through the dehydration process, while gentle tissues of flowers generally completely surrender their aromatic principals. The dehydration process alters the cell structure of the plant tissue, creating pores and cavities accessible to solvents and thus making the diffusion process reasonably quick. The plant material extracted fresh usually consists of flowers with gentle and thin petals which, despite the presence of water, offers low resistance to the diffusion.
The difficulty in conducting the extraction process becomes rather severe when hardy plant material is to be extracted but the aromatic values do not survive dehydration. Such is the case of a variety of coniferous plants and, in particular, various species of fir. The needles of the fir trees are specifically adapted to a very low rate of water evaporation therefrom and offer hard resistance to the penetration of the solvent. Thus, simple contact of fir needles with solvents results in very slow extraction. Due to the specific shape of the needles, a rough grinding is not efficient either, since breaking of the needle exposes only a small cross section to solvent penetration. It is, of course, possible to grind or to disperse fir needles into very fine particles. Such a process, however, is very expensive and for many reasons impractical.
The oleoresins of the coniferous trees are well known in the flavor, fragrance, cosmetic and pharmaceutical industries. The resin extracted from balsam fir (Abias balsamea L.) is the most widely known, and is even allowed to be used in food.
The presence of maltol in the coniferous trees in general, and in the balsam fir specifically, is well established in scientific literature. Maltol has also been reported to be in the bark of some species of larch trees. Maltol is present in latch bark in combined form to an extent varying from about 0.1 percent to about 2 percent by weight depending upon the bark layer and the season of harvest. The richest supply of maltol is found in the bark of roots of the larch trees although, for practical reasons, not much root bark is harvested. Large quantities of larch trees and bark containing maltol exist and are available primarily in the northwest part of the United States and southwest Canada. The bark is available at sawmills where it is stripped off of larch trees and stored in a pile, there to be burned for fuel or otherwise used if economical processes for recovering useful components therefrom can be found.
Limited quantities of fir balsam oleoresin are steadily produced by the extraction of dehydrated fir needles. The yield of oleoresin is rather low and so is the maltol content in it. The product is, therefore, costly and usually is employed only in expensive flavor and fragrance compositions. Due to its high cost and the low content of maltol, fir balsam oleoresin has not been seriously considered to be a practical source for recovery of maltol. Indeed, dehydration of the fir needles causes loss of essential oils, substantial reduction in the yield of oleoresin and a severe decrease in the maltol content of the product which is thereafter recovered. This result has been demonstrated by the applicant.
Despite the attractiveness of maltol and of oleoresins containing maltol, recovering significant amounts of maltol using known extraction techniques has proven to be difficult or disappointing.
Maltol is insoluble in non-polar hydrocarbons, which renders solvent extraction with such solvents unsuitable for recovering maltol-containing resin from plant material. Although maltol is soluble in hot water, the data in scientific and patent literature indicates that maltol cannot be efficiently recovered from plant material by hot water extraction.
Maltol shows substantial solubility in polar solvents such as acetone, alcohol, and the like. However, these solvents are water soluble and will dissolve not only maltol but also all the water contained in the fresh plant source material. This property makes subsequent recovery of the oleoresin or the maltol a difficult task. Utilization of water immiscible solvents (in which maltol is still soluble) for the extraction of fresh plant material by conventional techniques is restricted by the presence of water as described above.
Thus, there still remains a need for a method for recovering oleoresin, particularly maltol-containing oleoresin, from a source which is plant material.
It is an object of the invention to overcome the obstacles in recovery of oleoresins from source material including fresh plant material, and in particular from the foliage of coniferous species. It is a particular object of this invention to permit the removal of oleoresins, and particularly those containing maltol, from source material including plant material.